...And I still haven't spent $1000 on it

"Mark Tucker" (markbt73)
10/30/2020 at 18:05 • Filed to: None

I finally broke down and ordered a new exhaust manifold for the Toyota. I was going to hold off; it isn’t that loud, but then someone reminded me of the possibility of burned exhaust valves, which I hadn’t thought of. Better safe than sorry. Should be here in about a week. I also ordered a new stud set, so I w on’t have to wrestle with re-using the old rusty studs and nuts.

It was $73 including shipping from RockAuto, which brings my running total for this car, including purchase price but not gas or insurance, to a whopping $926. And that’s including two new front tires. It runs and drives fine, has cold AC and hot heat, and averages 29 mpg in city commuting. Who could ask for anything more, indeed?

Work still to be done, aside from the manifold: I need to get up the gumption to replace that fourth engine mount. It’s going to suck; the front subframe has to be unbolted and lowered to get it out, because unlike the other three, the rear mount has permanently-attached studs instead of bolts, and there’s no clearance to lift it out. Not looking forward to that.

I also have a cheap $22 eBay stereo to go in, in place of the barely-functional Pioneer CD player it came with. I’m giving up the CD player, but gaining an AUX input, bluetooth (if I want to bother), and an actual volume knob (the Pioneer has up/down buttons for the volume, which I can’t stand).

It’s not the most exciting thing on four wheels, nor the prettiest, but it’s turning into a stalwart companion, and a fantastic little runabout. Currently at 247,500 miles; I’m betting it will go to 300k. We’ll see.

DISCUSSION (11)

This is what we'll show whenever you publish anything on Kinja: > Mark Tucker
10/30/2020 at 18:23

I am 90-something % sure that burned exhaust valve thing is a myth. Scavenging is important for performance, but “needing back-pressure” is a lie agreed upon as far as I am aware.

Also... Please drive responsibly and with courtesy . 98% of the Corolla drivers I encounter should be barred from operating anything more substantial than a can opener.

bob and john > This is what we'll show whenever you publish anything on Kinja:
10/30/2020 at 18:35

IDK man, it makes sense to me.... to burn something you need fuel, oxygen, and an ignition source yea?

unburnt fuel from the combustion, o2 if its cracked or too short, and the heat is the ignition.

back pressure I think is something different. and can be used to play with torque curves IIRC. but I do not know enough to say yay or nay to that.

This is what we'll show whenever you publish anything on Kinja: > bob and john
10/30/2020 at 18:42

Maybe if you were running no exhaust manifold at all, but I somewhat doubt a leak is going to be enough to do it harm. That said, it might poison you as the fumes get sucked into the cowl at every stoplight s o fixing it is definitely a good idea. I just don’t know that the valves are the biggest worry under such a circumstance. I am far from an authority on the matter though.

bob and john > This is what we'll show whenever you publish anything on Kinja:
10/30/2020 at 18:44

also a fair point.

would be interesting to see a test on this. wonder how long it would take to notice issues.....

Snuze: Needs another Swede > This is what we'll show whenever you publish anything on Kinja:
10/30/2020 at 19:17

The scavenging / backpressure thing comes about because of ignorant rubes who don't understand fluid mechanics. They are related, and the ideal setup maximizes scavenging while minimizing backpressure.

Snuze: Needs another Swede > bob and john
10/30/2020 at 19:26

They are related. I also hate the term “ba ck pressure” - in engineering we call it pressure drop. T he exhaust leaves the chamber with a finite amount of energy (expressed as pressure) , and every bend, transition, and even length of straight pipe i t goes through uses up some of that energy.

Scavenging is using resonance to help suck exhaust gases out of the combustion chamber and down the pipe efficiently. To do this, you need a certain manifold design, which introduces pipe lengths, bends, etc., in other words things that add backpressure.

So the torque curve tuning you are talking about is designing manifolds to get resonances (scavenging) at a desired RPM, which boosts efficiency and therefore power. Its the difference between shorty headers, tri-Ys, and long tube headers. Shortys tend to maximize high RPM power, long tubes boost low end torque, and tri-Ys boost mid-range.

Header design is about balancing physical requirements (space constric tions) with tuning requirements (pipe length for desired RPM range) and doing it as efficiently as possible (minimizing bends, efficient collector design, etc.)

Mark Tucker > This is what we'll show whenever you publish anything on Kinja:
10/30/2020 at 19:38

I’m not a “Corolla driver.” I’m an MG driver who happens to have a Corolla as a daily driver. As such, I drive it quite quickly, but courteously and with skill and precision.

This is what we'll show whenever you publish anything on Kinja: > Mark Tucker
10/30/2020 at 19:50

Just signal and don’t leave a 15 car length space in front of you at all times and we’ll be fine.

Michael > This is what we'll show whenever you publish anything on Kinja:
10/31/2020 at 06:00

It’s from the oxygen in the fresh air interacting with the hot metal is the exhaust valve, from what I hear not the absence of back pressure.

So it's air getting in that's the problem, not exhaust getting out, same as o2 sensor

This is what we'll show whenever you publish anything on Kinja: > Michael
10/31/2020 at 10:22

But how much air is getting in from a leak when your engine is effectively an air pump forcing exhaust gasses out? I'd imagine it would have to be one hell of a leak to actually have an effect on the valves.

Michael > This is what we'll show whenever you publish anything on Kinja:
10/31/2020 at 14:07

Based on the pulsing nature of the exhaust stream, it actually can vacuum air in between pulses